1. Field of the Invention
This invention relates to an operation control device for a camera and more perticularly to a control mechanism which controls the opening action of shutter blades.
2. Description of the Prior Art
It has been known that an exposure control circuit can be greatly simplified for reduction in cost and that the degree of accuracy of exposure control can be improved to a great extent by an arrangement which makes the shutter opening characteristic (or relation of the open area to the opening time) arbitrarily adjustable to the characteristic of the exposure control circuit.
Therefore, for example, in the case of electromagnetically driven shutters arranged to directly open and close shutter blades by the reciprocative movement of a driving member which has a coil secured thereto, there have been proposed various methods for making the shutter opening characteristic arbitrarily adjustable. For example, Japanese Patent Publication No. SHO 51-5577 discloses a method of controlling the opening characteristic of a shutter by actuating a governor mechanism arranged to be responsive to the above-stated driving member. However, in accordance with this method, an electromagnetic driving force developed at the driving member is used to directly actuate the governor mechanism. Therefore, in order to stably operate the governor, the electromagnetic driving force to be applied to the driving member must be sufficiently large. Accordingly, this necessitates supply of a large current. This presents a problem as it is extremely difficult to supply such a large current from the output of batteries provided inside the camera body. Further, the supply of such a large current is not desirable as it shortens the lives of the batteries.
In the case of a camera of the kind incorporating therein an automatic focusing mechanism which is arranged to automatically bring a photographic lens into an in-focus state on the other hand, it is generally necessary to interrelate the automatic focusing (hereinafter called AF) mechanism with a shutter mechanism in such a way as to have an exposure begin after completion of an automatic focusing action. For this purpose, in a prior art method, the shutter mechanism has been arranged to be allowed to begin to operate by mechanically detecting completion of shifting of the photographic lens. In another prior art method, a timer circuit is arranged to begin a time defining action concurrently with commencement of a focusing action and a shutter mechanism is caused by this timer circuit to begin to operate after completion of the focusing action.
These methods of the prior art, however, have been unsatisfactory as they inevitably complicate the structural arrangement and the control circuit of a camera.